Nano-fabrication includes the fabrication of very small structures that have features on the order of 100 nanometers or smaller. One application in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. The semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate; therefore nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing continued reduction of the minimum feature dimensions of the structures formed. Other areas of development in which nano-fabrication has been employed include biotechnology, optical technology, mechanical systems, and the like.
An exemplary nano-fabrication technique in use today is commonly referred to as nanoimprint lithography. Nanoimprint lithography is useful in a variety of applications including, for example, fabricating layers of integrated devices such as CMOS logic, microprocessors, NAND Flash memory, NOR Flash memory, DRAM memory, or other memory devices, such as MRAM, 3D cross-point memory, Re-RAM, Fe-RAM, STT-RAM, and the like. Exemplary nanoimprint lithography processes are described in detail in numerous publications, such as U.S. Pat. No. 8,349,241, U.S. Pat. No. 8,066,930, and U.S. Pat. No. 6,936,194, all of which are hereby incorporated by reference herein.
A nanoimprint lithography technique disclosed in each of the aforementioned U.S. patents includes formation of a relief pattern in a formable (polymerizable) layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be coupled to a motion stage to obtain a desired positioning to facilitate the patterning process. The patterning process uses a template spaced apart from the substrate and a formable liquid applied between the template and the substrate. The formable liquid is solidified to form a solid layer that has a pattern conforming to a shape of the surface of the template that contacts the formable liquid. After solidification, the template is separated from the rigid layer such that the template and the substrate are spaced apart. The substrate and the solidified layer are then subjected to additional processes, such as etching processes, to transfer a relief image into the substrate that corresponds to the pattern in the solidified layer. The patterned substrate can be further subjected to known steps and processes for device fabrication, including, for example, oxidation, film formation, deposition, doping, planarization, etching, resist removal, dicing, bonding, and packaging, and the like.
Separation of the template from the solidified layer, however, can generate an electrostatic charge on one or both of the separated surfaces. This is due to the electrochemical potential difference between the two involved materials, a phenomenon also known to explain tribology effect. This electrostatic charge occurs as two different materials (here, the template and the solidified layer) are in friction with each other and then separate, thereby generating electrostatic charge. The electrostatic charge generated on the template and on the solidified layer, in turn, causes unwanted electrostatic attraction of different kinds of particulates from the air or surrounding environment. These particulates, once accumulated onto the template or solidified layer, in turn cause defects during subsequent imprinting and/or substrate processing, resulting in reduced imprint quality, device failure, template damage, and other associated problems.
Prior attempts to use ionized gas to discharge templates, such as depicted in U.S. Pat. No. 8,226,392, rely on establishing a flow of an ionized gas to the template. However, such ionized gas is understood to be generated by a corona (or high voltage) discharge from a metal conductor, which itself creates undesirable particles that can migrate to the template surface and cause damage and/or process defects. Such particles arise either through a direct metal sputtering mechanism or through thermal cracking of oxides or other deposits that accumulate on the conductor. However, efforts to alleviate the impact of generated particles, such as increasing the working distance from the template surface or providing for particle filtration end up reducing the effective ion concentration such that the effective discharge time becomes much longer than a typical imprint process time (i.e., a few seconds) to be practically useful for nanoimprint applications.
There are other techniques for generation of ionized air like x-rays, UV light, γ-radiation that are likewise unsuitable for nanoimprint lithography. While these techniques do not produce harmful particulates, they still do not produce enough ion concentration in air to yield an effective discharge rate for nanoimprint applications. Thus remains a need for more effective discharge systems and techniques for nanoimprint lithography.